1. Technical Field:
Heterogeneous formations are treated with potassium hydroxide by injecting into the more permeable strata of the formations an aqueous mixture containing solid potassium chloride followed by a concentrated potassium hydroxide solution.
2. Prior Art:
Sandstone formations containing fine particles can be damaged when such particles come in contact with an aqueous solution containing an ionic makeup different from that of the connate waters. Such can cause permeability reduction and reduce the flow of fluids to both injection wells and production wells. This phenomenon is especially prevalent in formations wherein the waters are becoming fresher. The "fine" particles are not limited to clays but include all swelling and potentially mobile fine particles within the sandstone pore bodies. Examples of such fine particles include clay minerals, large surface area silica (SiO.sub.2) minerals, feldspars, mica and barite.
Encroachment of the fresher waters in the formation can occur by an underlying aquifer, by enhanced oil recovery processes, by fluids used to treat near wellbore conditions, and the like instances. Swellable clays, such as montmorillionite having interstitial layers, swell when contacted with the fresher waters causing a reduction in permeability. Also, migratable clays, such as poorly cemented kaolinite and illite clay particles, can become detached from the sandstone formation during the flow of fresh water therethrough and can become trapped in the formation pore-throat openings reducing permeability and the flow of fluids therethrough. Often, encroachment of fresher brines into a formation containing clays results in occurrence of both types of permeability damage.
To overcome the above problem, U.S. Pat. No. 4,280,560 teaches the use of potassium hydroxide to stabilize sandstone formations containing water-sensitive fine particles. The potassium hydroxide interacts with the fine particles to render the particles immobile by permanently altering the silicate chemistry of the clays, thereby rendering them insensitive to fresh brines.
Treatment of stratified sandstone formation presents another problem. That is, treatment of such formations with the above technology can thieve the potassium hydroxide into the more permeable zones, leaving the less permeable zones untreated. A diverting fluid that is compatible with the formation and the potassium hydroxide treatment is needed. The diverting fluid should not have an adverse affect on the formation to be treated with KOH treatment and should permit a uniform treatment of the different permeable zones in the formation.